In the welding of one pipe section to another it is conventional to encircle one section with a clamp provided with a plurality of jacks which extend beyond the free end of the one pipe section and span the joint between the two pipe sections that are to be welded together. The jacks include jack screws which are adjustable radially of the clamp so as to move into engagagement with the second pipe section and support one end of the latter in confronting relation with the free end of the pipe section on which the clamp is mounted. The jack screws may be adjusted to align the second pipe section with the first pipe section and, in most cases, the jack screws may be adjusted so as to reform or reshape the configuration of the second pipe to match that of the first pipe. One pipe clamp construction of the kind described is disclosed in Dearman U.S. Pat. No. 3,653,574.
When preparing a clamp for use in aligning and reforming pipe sections the number of jacks that are required may vary considerably. For example, a clamp of the kind shown in the Dearman patent has the advantage of being usable with pipes of greatly differing diameters. Thus, three circumferentially spaced jacks may be adequate for use with pipes of relatively small diameter, but it may be necessary to use six or more jacks with pipes of larger diameter. Further, the number of jacks that may be required is dependent, to a large extent, on the extent of reformation which may be required to conform the confronting ends of the pipes. Thus, it may be necessary to provide more jacks for reforming than would be required for simply aligning two pipe sections.
When using a pipe clamp which is capable of accommodating pipes of greatly differing diameters, it has been the practice heretofore to fit the clamp with a number of jacks and apply the clamp somewhat loosely to one of the pipe sections. Thereafter, the individual jacks may be adjusted circumferentially of the pipe to the approximate positions they should occupy to enable the best results to be obtained. It is not always possible to locate the jacks initially as precisely as desired, so it often is necessary to adjust the jacks' positions. This necessitates loosening of the clamp and adjustment of the jacks, followed by retightening of the clamp. This procedure sometimes must be repeated several times before the jacks are positioned satisfactorily.
After a clamp has been fitted to one pipe section and the second pipe section is supported by the jacks in axial alignment with the first pipe section, it often occurs that there is a mismatch between the confronting surfaces of the two pipe sections. This may be due to differences in wall thicknesses or to an irregular bulge or indentation in one pipe wall. This mismatch commonly is referred to as a "hi-lo" condition, and such condition should be corrected as much as possible prior to welding operations. The best way in which to correct the hi-lo condition is by a jack which can act on one or the other of the pipe sections so as to eliminate or minimize the mismatch. However, in clamps of the kind in existence heretofore, an additional jack could not be applied to the clamp without loosening the latter. As a consequence, the alignment of the two pipes necessarily would be lost as a result of loosening of the clamp to enable it to accommodate another jack. Thus, considerable time has been taken up heretofore in aligning pipe sections and minimizing mismatches therebetween.
When using a clamp which carries a number of jacks that are intended to be spaced circumferentially about a pipe section when the clamp is applied, the combined weight of the clamp and jacks may be more than can be handled conveniently by one, or even two, workers. The handling of heavy clamps is fatiguing and, if more than one person is needed to apply a clamp to and remove it from a pipe section, the welding costs are increased. Further, the heavier the clamp the greater is the risk of injury to the person or persons using such clamp.
A principal object of the present invention is to provide a clamp construction which overcomes all of the problems referred to above.